1. Field of the Invention
The present invention relates to sleeves and sleeve segments, methods for manufacturing them and their use in methods of flexographic printing.
2. Description of the Related Art
Flexography is commonly used for high-volume runs of printing on a variety of supports such as paper, paperboard stock, corrugated board, films, foils and laminates. Packaging foils and grocery bags are prominent examples.
Today flexographic printing forms are made by both analogue imaging techniques such as a UV exposure through a film mask, e.g. EP 1594005 (DUPONT), and digital imaging techniques which include:                direct laser engraving on flexographic printing form precursors, e.g. US 2004/0259022 (BASF);        UV exposure through a LAMS mask, e.g. U.S. Pat. No. 6,521,390 (BASF) and U.S. Pat. No. 7,226,709 (KODAK), wherein LAMS means Laser Ablative Mask System;        Mask-less direct UV or violet exposure by laser or LED, e.g. U.S. Pat. No. 6,806,018 (MACDERMID); and        Inkjet printing e.g. EP 1428666 A (AGFA), US 2004/0131778 A (AGFA) and US 2006/0055761 (AGFA).        
Flexography is a “kiss impression” printing technology, i.e. the least possible squeeze between printing form and substrate. Two main types of flexographic printing forms can be distinguished: a sheet form and a cylindrical form. The cylindrical form or “sleeve” provides an improved lower change-over-time on press, better registration efficiency and is also well-suited for mounting on laser exposure equipment using a rotatable drum.
Flexographic printing sleeves are made by applying an elastomeric layer onto a plastic, a polymer composite or a metallic cylinder, or by winding a rubber ribbon around a plastic or metallic cylinder followed by a vulcanizing, grinding and polishing step. The forms preferable are seamless forms. As an alternative the elastomeric layer may be first applied on a flat support, which is then bent onto the carrier and bonded (see NYLOFLEX® Infinity Technology from BASF).
Flexographic printing sleeves can be used for flexographic printing of continuous designs such as in wallpaper, decoration, gift wrapping paper and packaging; as well as for flexographic printing of non-continuous designs such as labels.
Flexographic printing sleeves are frequently stored for future re-use. Combinations of different sleeves can be made on the same printing roll, including new flexographic printing sleeves and used flexographic printing sleeves.
A flexographic printing sleeve is usually mounted on a roll core by registering a female registration element on a radially projecting pin of the roll core. EP 510744 A (MILLER GRAPHICS) shows in FIG. 1 a roll core having a plurality of radially projecting pins on a regular distance which allows registering four sleeves on the roll core. As a drawback, the regular distance between the radially projecting pins result in a loss of printing surface between two sleeves and/or a limited set of fixed sizes for the sleeves depending on the distance between the radially projecting pins.
U.S. Pat. No. 7,107,907 (GOSS) discloses in FIG. 3 a rubber blanket cylinder (10) having air holes or air jets (14) and an air supply with a through-flow limiter to alter the air flow according to the axial position of three sleeve-shaped rubber blankets (12, 212, 312). The method of axially positioning or displacing rubber blanket sleeves on the cylinder does not disclose any means for registering the sleeve-shaped rubber blankets with respect to each other.
U.S. Pat. No. 5,974,972 discloses a printing carrier sleeve for mounting printing plates thereon, formed by cutting a sheet of flexible plastic material having opposite edges into a substantially rectangular shape of desired dimensions such that opposite edges are cut-away to provide complementary tabs and openings that interlock with each other, adhering printing plates on the sheet when the sheet is in a substantially flat condition, securing opposite edges of the sheet together in abutting relation so as to prevent air from passing between the opposite edges, and thereby forming the printing carrier sleeve in a cylindrical configuration, by placing a strip of tape on a forming cylinder, securing one edge of the rectangular sheet on the strip of tape on the cylinder, and wrapping the opposite edge of the sheet around the cylinder into abutting relation with the one edge to provide the interlocking arrangement.
A need exists to be able to register sleeves of different width in an easy manner on a roll core of a flexographic printing press without any costly adaptation of the printing press and avoiding any reduction of the total printing surface.